Why Does the Moon Look Different Every Night?

Some nights the Moon looks like a big bright circle. Other nights it looks like a thin, curved smile in the sky. Sometimes you can't see it at all! Have you ever wondered why the Moon keeps changing shape?

- Why the Moon only looks like it changes shape - What causes the Moon's phases - The names of a few Moon phases - How to track the Moon for two weeks

Here's a secret: the Moon is always a round ball of rock, just like it's always been. What changes is how much of the sunlit half we can see from Earth. The Moon travels all the way around Earth about once every 29 and a half days, and as it moves, we see different amounts of its sunny side.

When we can't see the Moon at all, that's called a new moon. About two weeks later, when we see the whole bright circle, that's a full moon. In between, we see a sliver or a half-circle. Every single phase happens in the same order, every single month, like clockwork.

On July 20, 1969, astronauts Neil Armstrong and Buzz Aldrin became the first people to walk on the Moon's rocky, dusty surface. They saw up close that the Moon isn't glowing on its own — it has no light of its own at all. Every bit of light we see from the Moon is really sunlight bouncing off it, like a giant mirror in the sky.